Shape Resonance at a Lifshitz Transition for High Temperature Superconductivity in Multiband Superconductors

Innocenti, Davide; Valletta, A.; Bianconi, A.

doi:10.1007/s10948-010-1096-y

Cited by 16 publications

(20 citation statements)

References 83 publications

(142 reference statements)

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“…17 There have been some theoretical efforts addressing these systems and the idea of incipient band pairing. For example, Innocenti et al 18 considered the effect of a Lifshitz transition on the critical temperature within 2-band BCS models corresponding to the case IB considered below. However, the most systematic work on Fe-based superconductors thus far is from Bang,19 who explored the evolution of T c across a Lifshitz transition in a model for Ba 1−x K x (FeAs) 2 .…”

Section: Introductionmentioning

confidence: 99%

Electron pairing in the presence of incipient bands in iron-based superconductors

et al. 2015

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Recent experiments on certain Fe-based superconductors have hinted at a role for paired electrons in "incipient" bands that are close to, but do not cross the Fermi level. Related theoretical works disagree on whether or not strong-coupling superconductivity is required to explain such effects, and whether a critical interaction strength exists. In this work, we consider various versions of the model problem of pairing of electrons in the presence of an incipient band, within a simple multiband weak-coupling BCS approximation. We categorize the problem into two cases: case(I) where superconductivity arises from the "incipient band pairing" alone, and case(II) where it is induced on an incipient band by pairing due to Fermi-surface based interactions. Negative conclusions regarding the importance of incipient bands have been drawn so far largely based on case(I), but we show explicitly that models under case(II) are qualitatively different, and can explain the non-exponential suppression of Tc, as well as robust large gaps on an incipient band. In the latter situation, large gaps on the incipient band do not require a critical interaction strength. We also model the interplay between phonon and spin fluctuation driven superconductivity and describe the bootstrap of electron-phonon superconductivity by spin fluctuations coupling the incipient and the regular bands. Finally, we discuss the effect of the dimensionality of the incipient band on our results. We argue that pairing on incipient bands may be significant and important in several Fe-based materials, including LiFeAs, FeSe intercalates and FeSe monolayers on strontium titanate, and indeed may contribute to high critical temperatures in some cases.

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Section: Introductionmentioning

confidence: 99%

Electron pairing in the presence of incipient bands in iron-based superconductors

et al. 2015

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“…Theoretical proposals have been put forward that strong T c enhancement can be achieved close to Lifshitz transition in striped 32,33 and layered systems 34 . Superconductivity in two-band models close to a Lifshitz transition is also being studied 27,35,36 . Recent experiments on monolayer FeSe 37 do suggest enhancement of superconductivity by a Lifshitz transition.…”

Section: Introductionmentioning

confidence: 99%

s+is superconductivity with incipient bands: Doping dependence and STM signatures

et al. 2017

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Motivated by the recent observations of small Fermi energies and comparatively large superconducting gaps, present also on bands not crossing the Fermi energy (incipient bands) in iron-based superconductors, we analyze the doping evolution of superconductivity in a four-band model across the Lifshitz transition including BCS-BEC crossover effects on the shallow bands. Similar to the BCS case, we find that with hole doping the phase difference between superconducting order parameters of the hole bands change from 0 to π through an intermediate s + is state, breaking time-reversal symmetry (TRS). The transition, however, occurs in the region where electron bands are incipient and chemical potential renormalization in the superconducting state leads to a significant broadening of the s + is region. We further present the qualitative features of the s + is state that can be observed in scanning tunneling microscopy (STM) experiments, also taking incipient bands into account.

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“…In addition, "conventional" sign-changing s ± states with gaps of different signs on the incipient hole band and the electron Fermi pockets are possible [14][15][16]. In oneband systems, when electronic states are moved off the Fermi level, the pairing is rapidly suppressed.…”

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confidence: 99%

Effect of nonmagnetic impurities ons±superconductivity in the presence of incipient bands

Chen¹,

Mishra²,

Maiti³

et al. 2016

Phys. Rev. B

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Several Fe chalcogenide superconductors without hole pockets at the Fermi level display high temperature superconductivity, in apparent contradiction to naive spin fluctuation pairing arguments. Recently, scanning tunneling microscopy measurements have measured the influence of impurities on some of these materials, and claimed that non-magnetic impurities do not create in-gap states, leading to the conclusion that the gap must be s++, i.e. conventional s wave with no gap sign change. Here we critique this argument, and give various ways sign-changing gaps can be consistent with the absence of such bound states. In particular, we calculate the bound states for an s± system with a hole pocket below the Fermi level, and show that the nonmagnetic impurity bound state energy generically tracks the gap edge Emin in the system, thereby rendering it unobservable. A failure to observe a bound state in the case of a nonmagnetic impurity can therefore not be used as an argument to exclude sign-changing pairing states.Introduction -Superconductivity in the Fe-based superconductors[1] is thought to be controlled by local Coulomb interactions that give rise to repulsive effective interactions between band electrons [2][3][4]. In contrast to other materials classes where similar unconventional pairing mechanisms are at work, the Fe-based systems have a Fermi surface consisting of several small pockets around high symmetry points in the Brillouin zone. Pair scattering between Γ-centered hole pockets and M -centered electron pockets, was proposed early on as a plausible mechanism, with interpocket repulsion enhanced over intrapocket by electronic spin fluctuations. Somewhat later, new materials subfamilies were discovered (chiefly the FeSe intercalates [5][6][7] and monolayer FeSe on SrTiO 3 (STO) [8]), where doubt was cast on this particular pairing mechanism because of angle-resolved photoemission (ARPES) measurements that showed that the hole bands were not present at the Fermi surface, but instead had band maxima 50-100meV below ("incipient" bands).

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Shape Resonance at a Lifshitz Transition for High Temperature Superconductivity in Multiband Superconductors

Cited by 16 publications

References 83 publications

Electron pairing in the presence of incipient bands in iron-based superconductors

Electron pairing in the presence of incipient bands in iron-based superconductors

s+is superconductivity with incipient bands: Doping dependence and STM signatures

Effect of nonmagnetic impurities ons±superconductivity in the presence of incipient bands

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